1. Field of the Invention
The present invention relates to a magnetic head that is used for writing data on a recording medium and a method of manufacturing such a magnetic head, and to a method of forming a patterned layer.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Like magnetic heads for longitudinal magnetic recording, magnetic heads for perpendicular magnetic recording typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head comprises a pole layer that produces a magnetic field in the direction perpendicular to the surface of the recording medium. The pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in a medium facing surface that faces toward the recording medium. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in write characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the write characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, are degraded. It is therefore required to achieve better write characteristics as the track width is reduced. Here, the length of the track width defining portion taken in the direction orthogonal to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has a medium facing surface that faces toward a recording medium. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt called a skew of the magnetic head is created with respect to the tangent of the circular track, in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew is created, problems arise, such as a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erase) or unwanted writing is performed between adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the problems resulting from the skew as described above, as disclosed in U.S. Pat. No. 6,504,675 B1 and U.S. Patent Application Publication No. US2006/0002014 A1, for example. According to this technique, the end face of the pole layer located in the medium facing surface is made to have a shape in which the side located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising the pole layer and a shield is also known, as disclosed in U.S. Pat. No. 4,656,546 and U.S. Patent Application Publication No. US2006/0002014 A1, for example. In the medium facing surface of this magnetic head, an end face of the shield is located forward of the end face of the pole layer along the direction of travel of the recording medium with a specific small space therebetween. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head the shield has a function of preventing a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and extending in directions except the direction orthogonal to the surface of the recording medium. In addition, the shield has a function of returning a magnetic flux that has been generated from the end face of the pole layer and has magnetized the recording medium. The shield-type head achieves a further improvement in linear recording density.
Typically, the pole layer is patterned through the use of photolithography. For example, to form the pole layer by frame plating, a frame made of a photoresist layer patterned by photolithography is formed, and the pole layer is formed in this frame by plating. After forming the pole layer by frame plating in such a manner, the track width is reduced in some cases by etching both side portions of the track width defining portion through dry etching such as ion beam etching. When the pole layer is formed by patterning a magnetic layer by etching, an etching mask made of a photoresist layer patterned by photolithography is formed on the magnetic layer, and the magnetic layer is selectively etched using the mask to form the pole layer.
In the course of manufacturing process of magnetic heads, a number of magnetic head elements to be the magnetic heads are formed in a single substrate (wafer). The substrate in which the magnetic head elements are formed is cut such that the surface to be the medium facing surfaces appears. This surface is then polished to form the medium facing surfaces.
When the pole layer is patterned through the use of photolithography as previously described, it is likely that the patterned resist layer goes out of a desired shape due to the effects of, for example, reflection of light off the base layer when the photoresist layer is exposed. Consequently, it is also likely that the pole layer goes out of a desired shape. In particular, it is likely that portions of the side portions of the pole layer near the boundary between the track width defining portion and the wide portion go out of desired shapes.
Reference is now made to FIG. 42 to describe a first problem resulting from a deviation of the pole layer from its desired shape. FIG. 42 illustrates an example of shape of the top surface of the pole layer. FIG. 42 illustrates a neighborhood of the boundary between a track width defining portion 201 and a wide portion 202 of the pole layer before the medium facing surface is formed. In FIG. 42 ‘ABS’ indicates a region in which the medium facing surface is to be formed, ‘TW’ indicates the physical track width, and ‘NH’ indicates the neck height as designed.
When the pole layer is patterned through the use of photolithography, as previously described, it is likely that the pole layer goes out of a desired shape. As a result, particularly when the neck height NH is small, it is likely that the track width defining portion 201 forms a shape in which the width increases as the distance from the medium facing surface increases, as shown in FIG. 42.
When the track width defining portion 201 has a shape as shown in FIG. 42, the neck height is strictly the length between the region ABS and the point at which the width of the track width defining portion 201 starts to be greater than the width thereof taken in the region ABS. However, if the neck height is thus defined, it is difficult to precisely determine the neck height when the track width defining portion 201 has the shape as shown in FIG. 42. Therefore, the neck height is defined as will be described below when the track width defining portion 201 has the shape as shown in FIG. 42. In the top surface of the pole layer, the intersection point of imaginary lines L11 and L12 is defined as P. The imaginary line L11 passes through the intersection point of the region ABS and the side portion of the track width defining portion 201, and extends in the direction orthogonal to the region ABS. The imaginary line L12 extends from a straight line portion of the side portion of the wide portion 202 connected to the side portion of the portion 201 and extends in the direction in which the straight line portion extends. The distance between the region ABS and the intersection point P is defined as the neck height. The neck height as thus defined is nearly equal to the neck height NH as designed.
When the track width defining portion 201 has the shape as shown in FIG. 42, if the location of the medium facing surface goes out of a desired location and the neck height then goes out of a desired value, there is a possibility that the physical track width TW is out of a desired value, too.
An example of method of manufacturing magnetic heads will now be described. First, components of a plurality of magnetic heads are formed on a single substrate to fabricate a magnetic head substructure in which a plurality of rows of pre-head portions that will be the magnetic heads later are aligned. Next, the magnetic head substructure is cut to fabricate a head aggregate including a single row of the pre-head portions. Next, a surface formed in the head aggregate by cutting the magnetic head substructure is polished (lapped) to form the medium facing surfaces of the pre-head portions that the head aggregate includes. Next, flying rails are formed in the medium facing surfaces. Next, the head aggregate is cut so that the pre-head portions are separated from one another, and the magnetic heads are thereby formed.
An example of method of forming the medium facing surfaces by lapping the head aggregate will now be described. In the method the head aggregate is lapped so that the MR heights of a plurality of pre-head portions are made equal while the resistances of a plurality of MR elements that the head aggregate includes are detected. The MR height is the length of each of the MR elements taken in the direction orthogonal to the medium facing surface.
According to the method of forming the medium facing surfaces as described above, it is possible to form the medium facing surfaces so that the MR heights are of a desired value. As a result, according to the method, a portion of each medium facing surface at which an end of the MR element is exposed is placed at a desired location. Furthermore, if the angle formed between the medium facing surface and the top surface of the substrate is 90 degrees, a portion of the medium facing surface at which an end face of the track width defining portion is exposed is placed at a desired location, too. As a result, the neck height is of a desired value, too.
In prior art, however, the angle formed between the medium facing surface and the top surface of the substrate is other than 90 degrees in some cases. This is caused by a misalignment between the head aggregate and a jig that supports the head aggregate when the aggregate is lapped. If the angle formed between the medium facing surface and the top surface of the substrate is other than 90 degrees, the portion of the medium facing surface at which the end face of the track width defining portion is exposed is placed at a location other than the desired location even though the portion of the medium facing surface at which the end of the MR element is exposed is placed at the desired location. As a result, the neck height is of a value other than the desired value. In FIG. 42 the range indicated with numeral 203 shows a range of variations in location of the portion of the medium facing surface at which the end face of the track width defining portion is exposed.
As previously described, if the neck height is of a value other than the desired value, the physical track width is of a value other than the desired value, too. As thus described, the problem is that there are some cases in prior art in which the portion of the medium facing surface at which the end face of the track width defining portion is exposed is placed at a location other than the desired location, and the physical track width is of a value other than the desired value, accordingly. As a result, the yield of magnetic heads is reduced. The smaller the desired neck height, the more noticeable is this problem.
A second problem resulting from a deviation of the pole layer from its desired shape will now be described. In a region near the boundary between adjacent ones of the tracks of the recording medium, magnetic signals written on each of the tracks are weakened by the effect of magnetic signals written on each of the adjacent ones of the tracks. One of write characteristics of a magnetic head is a signal-to-noise ratio (that may be hereinafter referred to as an SN ratio) obtained in a state in which magnetic signals are written on a plurality of adjacent tracks. The smaller the width of the above-mentioned region near the boundary between adjacent ones of the tracks in which the magnetic signals are weakened, the greater is the SN ratio. On the contrary, the greater the width of this region, the smaller is the SN ratio.
The physical track width of the magnetic head is defined by the width of the end face of the track width defining portion located in the medium facing surface. Typically, the effective track width corresponding to the width of the region in which magnetic signals are actually written on the recording medium is greater than the physical track width. Here, the greater the difference between the effective track width and the physical track width, the greater is the above-mentioned region near the boundary between adjacent ones of the tracks in which the magnetic signals are weakened. The above-mentioned SN ratio is thereby reduced.
The difference between the effective track width and the physical track width greatly varies depending on the shape of the pole layer. In particular, if the shape of the track width defining portion 201 is such one that the width increases as the distance from the medium facing surface increases as shown in FIG. 42, the difference between the effective track width and the physical track width increases, and the above-mentioned SN ratio is thereby reduced. This is the second problem resulting from a deviation of the pole layer from its desired shape. This problem becomes more noticeable, too, as the desired neck height is reduced.
A method called optical proximity correction (hereinafter referred to as OPC) has been known as a method of making the shape of a resist layer patterned by photolithography closer to a desired one. For the OPC, a photomask used for exposing an unpatterned resist layer is such one that the shape of the boundary between a translucent portion and a light-tight portion is adjusted. However, even though the OPC is employed in prior art, it is difficult to form the shapes of the portions of the side portions of the pole layer near the boundary between the track width defining portion and the wide portion with higher precision.